Ports and Interfaces > USB
usb vcp mode
madhukar:
iam implementing a vcp type communication on a STM32L0 CONTROLLER device
relevant vcp driver supplied by ST IS INSTALLED ON host pc.
our device is coincell powered and we keep the usb in powerdown mode all the time to reduce power consumption
on connecting with pc we sense the vbus and an interuput is used to start the usb port
when i connect the device to pc it is detected 50% times and fails other times.
at times an yellow triangle appears in device manager showing a wrong com port and the communication does not work.
please suggest a way out to make a robust system.
is there a way to ask the host to initiate detection process from device side?
towlerg:
If you don't already try adding a serial number.
bpaddock:
--- Quote from: madhukar on November 03, 2017, 02:29:12 am ---iam implementing a vcp type communication on a STM32L0 CONTROLLER device
...
our device is coincell powered ...
--- End quote ---
If you power it externally, for at least this test, does anything change?
Jan Axelson:
Assuming USB 2.0 full or high speed, the host (actually the upstream hub) detects device attachment by detecting the voltage at the pull-up resistor on D+.
So the pull-up should be switched out until the device is ready to begin communicating.
Except for some devices with weak or dead batteries, the device must bring the pull-up line high within 1 s after detecting that VBUS is at least 0.8 V.
madhukar:
DELAY ON D+ HAS WORKED
THANKS JAN. IT IS NOW WORKING.
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